Communications installations utilize relay racks for a variety of purposes. One of such purposes is to support auxiliary equipment. To this end, it is often desirable to provide a shelf on a relay rack to receive and support a variety of types of equipment. The space requirements in a communications installation demand that space be optimized. In addition, it is desirable for a shelf on a relay rack to be easily mounted on the relay rack and securely positioned. It is also desirable to provide a shelf for use on a relay rack which may be installed by a single individual to make the installation of the shelf efficient. Furthermore, a relay rack with a shelf must have a high degree of stability.